1. Field of the Invention
The present invention relates to an information recording carrier for use in system for recording and/or reproducing information by optical means.
2. Description of the Related Art
Conventionally, a system for reading out information by moving the information recording carrier relatively has been available and optical means, magnetic means and electrostatic capacity means are used for reproducing information therefrom. Of them, the system for recording and/or reproducing information by the optical means has prevailed widely in daily life (“recording/reproducing” mentioned here means three statuses, namely, only recording, only reproduction or recording and reproduction).
For example, as a recording/reproducing type information recording carrier using beam having wavelength λ=650 nm, DVD-RAM, DVD-RW (“DVD” means digital versatile disc) and the like are available.
Although the recording/reproducing type information recording carriers have been developed as actual products and marketed, the technology for burying address information into such recording/reproducing type information recording carrier effectively has been still being developed and a next generation information recording carrier will need improvement of the conventional address recording technology or a new address recording technology.
The first purpose for burying address information effectively is to bury address information at a low error rate without substantially decreasing an area provided for recording/reproducing, and the second purpose is to bury the address information by suppressing the error rate of recording mark so that buried address information never interferes with a main recording/reproducing region.
As for the first object, for example, in the information-recording carrier employing a header type address represented by DVD-RAM (DVD rewritable), the address information is recorded by pit row (called header) by cutting a main recording/reproducing region. Because the header has the same format as the reproduction dedicated information-recording carrier, the error rate of the address information is suppressed very low.
However, because recording cannot be achieved in this header region, the entire capacity of an information-recording carrier whose area is limited drops. Thus, address recording system not using the header is necessary.
As for the second object, in the information recording carrier employing inter-groove address pits represented by for example, DVD-RW (DVD rerecordable), the recording/reproducing region is continuous and has no cut area. Therefore, the first object can be satisfied.
However, the marks recorded in the groove as a recording/reproducing region interferes with the inter-groove address pits upon reproduction so that the error rates of both the marks and pits rise.
FIG. 1 is a plan view showing a enlarged minute pattern on a DVD-RW.
As the minute pattern, plural substantially parallel groove continuities 150 are formed. Each of the continuities 150 is comprised of a groove 151 and an inter-groove portion 152 such that both are formed substantially parallel to each other.
In the meantime, the groove 151 and the inter-groove portion 152 have different heights (a difference in height is for example, λ/14n when the recording wavelength is λ and the refractivity of a recording light transmitting member is n). Address information is prepared as shapes of pits and is widely dispersed in the inter-groove portion 152 and recorded. In other words, the inter-groove address pit 153 is arranged on the inter-groove portion 152 so that the address information is recorded.
On the other hand, since the recording by a user is performed on the groove 151 and is not physically overlapped with the inter-groove address pit 153, the user recording capacity is not reduced. There is, however, a moment when the user recording mark and the inter-groove address pit 153 become to be in parallel and at this moment the user recording mark and the inter-groove address pit 153 interfere with each other.
Accordingly, both the error rate of the user recording and the error rate of address increase and thus the second object cannot be satisfied.
In view of the problems to be solved, the first object is to bury address information at a low error rate without reducing the area provided for recording/reproduction, the second object is to bury the address information so as not to interfere with the user recording mark.
Particularly, the present invention proposes a novel address recording method without using the header pit employed in DVD-RAM and the inter-groove address pit employed in DVD-RW. At this time, it is considered in this method that the buried address information does not interfere with another address information adjacent thereto.
Further, the present invention considers that gallium nitride base compound semiconductor light emission device (for example, described in Japanese Patent No. 2778405) recently developed to raise the recording density of the information recording carrier, that is, short-wave laser which emits light in the vicinity of λ=350 to 450 nm produces more noise than a conventional laser.
Further, although technology for forming the information recording carrier in multiple layers so as to increase its recording capacity has been well known, it must be considered that noise in the reproducing system is increased by this multiple-layers.
Further, the present invention aims at corresponding to a recently developed light transmission layer incident information recording carrier from viewpoints of physical structure.